Recently, motor-driven vehicles have been manufactured and have received very much attention from the viewpoint of reduced environmental loading. In such a vehicle, basically, a fuel cell supplies electric power to a motor, thereby the motor is driven. At this time, since the fuel cell generates water without containing impurities, the emission of the water does not increase the environmental loading, which is greatly supported in the current environmental society.
When a motor is driven by a fuel cell, maximum electric power cannot be supplied to the motor from the fuel cell immediately after a switch is turned on. Consequently, with such a configuration, acceleration of the vehicle is very slow. Therefore, it is devised that a fuel cell and an electrochemical capacitor are coupled in parallel to a motor. That is to say, when electric power necessary for the motor is not sufficiently supplied from the fuel cell alone, for example, during acceleration of the vehicle, electric power is supplied from the electrochemical capacitor. Thus, acceleration performance can be improved.
In the case where the electrochemical capacitor is used in order to supplement the shortage of acceleration, however, capacitance of the electrochemical capacitor is reduced due to the long-term use. When the electrochemical capacitor is used for a long time, in a positive electrode and a negative electrode, ions approaching the positive and negative electrodes cause dielectric breakdown. Thereby, reaction products are generated on the surfaces of the positive and negative electrodes. When the reaction products are attached to the positive and negative electrodes, the surface areas of the positive and negative electrodes are reduced. Therefore, the number of ions in electrolyte attracted to the positive and negative electrodes is reduced, so that capacitance of the electrochemical capacitor is reduced. If such a reduction of capacitance is allowed to stand, the capacitance of the electrochemical capacitor is further reduced. When the capacitance of the electrochemical capacitor is reduced in this way, acceleration performance of the vehicle is deteriorated.